The disclosed invention relates to ink jet printing devices, and more particularly to improved techniques for driving a print carriage.
An ink jet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes called xe2x80x9cdot locations,xe2x80x9d xe2x80x9cdot positions,xe2x80x9d or xe2x80x9cpixelsxe2x80x9d. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.
Ink jet printers print dots by ejecting very small drops of ink onto the print medium, and typically include a movable print carriage that supports one or more printheads each having ink ejecting nozzles. The print carriage is slidably supported by a slider rod and traverses back and forth over the surface of the print medium. While the print carriage moves back and forth, the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed. Typically, a plurality of rows of pixels are printed in each traverse or scan of the print carriage. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using thermal printhead or piezoelectric technology. For instance, two earlier thermal ink jet ejection mechanisms are shown in commonly assigned U.S. Pat. Nos. 5,278,584 and 4,683,481. In a thermal system, an ink barrier layer containing ink channels and ink vaporization chambers is disposed between a nozzle orifice plate and a thin film substrate. The thin film substrate typically includes arrays of heater elements such as thin film resistors which are selectively energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized heater element. By selectively energizing heater elements as the printhead moves across the print medium, ink drops are ejected onto the print medium in a pattern to form the desired image.
Typically, a print carriage is caused to move back and forth by a carriage motor that drives an endless belt attached to the carriage. A consideration with attaching a drive belt to a print carriage is the impartation of undesired twisting forces to the print carriage assembly, which detrimentally affect print quality. Another consideration is the difficulty and impracticality of attaching the belt at a location that is optimal for carriage dynamic stability, since other components are also mounted on the carriage and since the belt attachment apparatus tends to occupy a relatively large amount of space on the print carriage.
There is accordingly a need for an improved mechanism for driving a print carriage.
The disclosed invention is directed to a print carriage drive assembly that includes a print carriage that is slidably supported on a slider rod for reciprocating movement, a reciprocating belt configured to act like a spring, a belt clamp attached to the belt, and a compliant coupling structure connected between the belt attach and the print carriage for applying a driving force to the carriage at a location that is displaced from the belt and which can be selected to reduce moments that would otherwise be caused by application of the driving force. In accordance with a further aspect of the invention, the compliant coupling structure has rotational freedom of movement relative to the print carriage that allows small linear displacements along a carriage axis between the reciprocating belt and the print carriage, whereby the belt and the coupling structure cooperate to isolate the carriage from driving force variations.